Process for the transportation of acid gases in natural gas liquids streams

ABSTRACT

LIQUIDS STREAM, TRANSPORTING THE DRIED ACID GAS AND NATURAL GAS LIQUIDS MIXTURE THROUGH A PIPE LINE TO A SEPARATION ZONE AND RECOVERING THEREIN THE ACID GAS CONTENT OF SAID GAS AND NATURAL GAS LIQUIDS MIXTURE.   A PROCESS FOR THE PREPARATION AND TRANSPORTATION OF AN AT LEAST PARTIALLY DEHYDRATED ACID GAS/NATURAL GAS LIQUIDS MIXTURE IS DESCRIBED WHICH COMPRISES SEPARATING A SOUR FIELD NATURAL GAS STREAM INTO A NATURAL GAS STREAM, AN ACID GAS STREAM AND A NATURAL GAS LIQUIDS STREAM, DYRING THE SEPARATED ACID GAS STREAM AND NATURAL GAS LIQUIDS STREAM, MIXING THE DRIED ACID GAS STREAM AND DRIED NATURAL GAS

United States Patent G 3,812,030 PROCESSFOR THE TRANSPORTATION OF ACID GASES IN NATURAL GAS LIQUIDS STREAMS Harris A. Clay, Bartlesville, Okla., assignor to Phillips Petroleum Company Filed Oct. 13, 1972, Ser. No. 297,361

Int. Cl. C10g 5/00 U.S. Cl. 208--340 9 Claims ABSTRACT OF THE prscwsumz A process for the preparation and transportation of an at least partially dehydrated acid gas/natural gas liquids mixture is described which comprises separatng a sour This invention relates to a process for the fractional separation of a sour field natural gas stream, dehydration and transportation of the resultng acid gas stream and the natural gas liquids stream, and the recovery of the elemental sulfur contained within the dehydrated acid gas and natural gas liquids mixture.

The acid gas content of a sour field natural gas stream is customarily separated from the leannatural gas after treating the field natural gas streams to recover the natural gas liquids. Providing the sulfur content of the acid gas stream is suflicient to perrnit economical recovery of elemental sulfur, a sulfur plant is frequently located at or near the sour ce of the sour natural gasstream. In the absence of suicie nt field acid gas sulfur to justify a sulfur plant adjacent or close to the natural. gas field, the acid gases are frequently oxidized to sulfur dioxide and vented to the atmosphere. In view of the continuing public and private interest in reducing air pollution, it is anticipated that the disposal of acid gas sulfur in the form of sulfur dioxide near the natural gas fields may soon be restricted or prohobited entirely. Accordingly, determination of suitable alternatives to venting of acid gases to the atmosphere at or near the natural gas fields or to erecting uneconomical inefficent, underszed sulfur recovery production facilities near the field natural gas source is of immediate interest to both the general public and the natural gas processing industry at large.

According to this invention, a process is provided comprsing the fractional separation of a sour field natural gas stream into a lean natural gas stream, an acid gas stream, and a natural gas liquids stream, dehydration of the acid gas and natural gas liquids streams, combination of the dehydrated acid gas and natural gas liquids streams, and transportation of the dehydrated mixture through a pipe line to location having facilities for recovery of the acid gas content of said mixture.

It is an object of this invention to provide a process for the separation and transportation of the acid gas content of field natural gas streams from a natural gas processing plant to a distant process center for the recovery therefrorn of elemental sulfur or sulfur com- 3,812,030 Patented May 21, 1974 ice object is to provide a process for the trai1sportationof acid gas components to a process center via existingnatural gas liquids pipe lines. Another object is to avoid venting of acid gas components and/or the oxides thereof. to the atmosphere. These and other objects will be ap parent from the written description, the drawing, and the appended claims.

In general, in accordance with the practice of this invention, the sour field natural gas stream is fractionally separated at a natural gasfield processing installation to provide a lean natural gas stream, an acid gas stream and a natural gas liquids stream. After separation, both the acid gas stream and the natural gas liquids stream are suitably and sufliciently dehydrated in order to reduce the water content of any combination of the acid gas and natural gas liquids to quanttes which limit any ap preciable formation of corrosive acids, such as hydrosulfurie acid or carbonic acid. Generally, acidgas and natural gas liquids mixtures that are substantially free of water, e.g., contain less than p.p.m. of water, can be transported over long distances to another separation zone without promoting or significantly affecting the service life of the equipment, i.e., pumps, pipe lines, etc. employed for transportation of the mixtures to the other separation zones. Preferably, the acid gas and natural gas liquids streams are suflciently dried to provide stream mixtures containing about 50 p.p.m. or less water, more preferably mixtures essentially free of water, i.e., about 1 p.p.rn. of water. Still more preferred are mixtures of acid gases and natural gas liquids which contain no measurable amount of moisture, i.e., lessthan 1 p.p.m.

The process of this invention will be described in greater detail with reference to the accompanying drawing which llustrates by means of a schematic drawing an exemplary process embodyng the present invention.

Referring now to the single FIGURE, in which the separation proceses employed in the separation zones comprise any of the fundamental separation processes common and well known to those skilled in the art, 2. sour field natural gas stream 1 containing natural gas, natural gas liquids, and acid gas constituents is introduced into separation zone I wherein a natural gas liquids stream 2 is separated from a sour lean natural gas stream 3 which contains methane, and a small amount of ethane and heavier hydrocarbons not removed in zone 1, and acid gases, such as hydrogen sulfide, carbon dioxide and occasionally carbonyl sulfide. Stream 3 may also contain nitrogen and helium. The sour lean natural gas stream 3 is passed to separation zone II where it is separated into an essentially acid gas tree lean natural gas product stream 4 suitable for delivery to a pipe line as domestc fuel and an acid gas stream 5. The acid gas stream 5 passed to drying zone III where it is dried to produce dehydrated acid gas stream 6.

The natural gas liquids stream 2 is dried in drying zone IV to produce a dehydrated natural gas liquids stream 7. Streams 6 and 7 are mixed to produce stream 8 which at this point is sufliciently dry to be essentially noncorrosive. A moisture content of 50 p.p.m. or less is generally satisfactory. Liquid stream 8 may then be transported through a pipe line for long distances to separation zone V where it is separated into an acid gas free natural gas liquids stream 9 and an acid gas stream 10. The acid gas stream 10 may then be sent to a plant 11 wherein the acid gas si1lfur content is recovered as element al su1fi1r, sulfu1' dioxide; sulfuric acidor other valuable products. Plant 11 can employ a typical sulfur recovery process, e.g., see Petroleum Refining Engineering, W. L. Nelson, 4th Edition, pages 756-758, 1958, McGraw Hill Inc., N.Y.

Examples of typical fundamental separation processes well known to the art that can be employed in the various process zones dcscribed hereinbefore are as follows:

Zone I, oil absorption of natural gas liquids followed by steam strpping (see Natural Gas and Natural Gaspline, R. L. Huntington, 1st Edition, pp. 76 77 1950,

McGraw Hill Inc., N.Y.)

Zone II, absorption of acid gases employing mono and diethanol amines or other suitable solvents followed by steam stripping (see Perrys Handboek for Chemical Engineers, 4th Edtion, page 14-2, 1963, McGraw Hill Zone III, separation of water from the acid gases em ploying bauxite driers which can be conveniently regenerated, or any other suitbale drying process (see Natural Gas and Natural Gasoline, ibid., pp. 348-354).

Zone IV, separation of water trom natural gas liquids employng bauxite driers which can be conveniently regenerated (see Petroleum Refining Engineering, W. L. Nelson, 4th Edition, page 234, 1958, McGraw Hill Inc. N.Y.).

Zone V, any absorption process based on pressure-temperature relationships, such as those concisely sum marized in Perrys Handbook for Chemical Engineering, 4th Edition, page 14-2, 1963, McGraw Hill Inc. N.Y.

a mixture of acid gas and natural gas liquids which comprises the steps:

passing a sour natural gas stream comprising natural gas, acid gas, and natural gas liquids into a first sepaation zone,

separating and withdrawing from sad first separation zone a first eflluent stream comprising a lean natural gas, a second effluent stream comprising an acid gas,

and a third eflluent stream comprsingnaturahgas liquids,

dehydrating sad second and third efliuent streams,

passing an admixture of the resulting dehydrated natural gas liquids and the resulting dehydrated acid gas over a long distance to a second separation zone, and

separating and withdrawing from sad second separation zone an acid gas stream and a natural gas liquids stream.

2. A process in accordance. with claim 1, wherein sad admixtureissubstantially free of water.

3. A process in accordance with claim 1 wherein the misture content of the admixture is about 50 p.p.m. or 1ess.

4. A process in accordance with claim 1, wherein the admixture contains no measurable amounts of water.

5. A process in accordance with claim6 further coinprising recovering the elemental sulfur content of sad acid gas stream.

6. A process in accordance with claini l wherein the step of dehydrated sad second and third efiluent strcams comprising passing sad second ffluent stream into a first drying zone and withdrawing therefrom a dehydrated acid gas stream, and passing sad third effluent stream into a second drying zone and withdrawing therefrom a dehydrated natural gas liquids stream.

7. A process inaccordnce with claim 6 wherein sad admixture is obtained by admixing at least a portion of sad dehydrated acid gas stream with at least aportion of sad dehydrated natural gas liquids stream.

-8. A process in accordance with claim 7 further comprising passing at least a portion of sad acid gas stream withdrawn from sad second separation zone into a third sparation zone and withdrawing from sad thrd separation zone a first product stream comprising elemental sulfur.

9. A process in accordance with claim 1 wherein the admixture is essentially free of water.

Refereuces Cited UNITED STATES PATENTS 3,630666 12/1971 Kunkel 208340 1,762,423 6/1930 Scharpenberg 20s3 40 HERBERT LEVINE, Primary Examinei U.S. C1. X.R.

UNI'IED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIN PATENT NO. 1 3,812030 Harris A. |t is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown betow:

Column 4, line 19, delete "6" and insert 3 column 4, line 23, delete "dehydrated" and insert dehydrating column 4, line 24, delete "comprising" and insert comprises Q ,5gnccl and ,5caled ths Thirty-first Day of August 1976 Attest:

RUTH C. MASON C. MARSHALL DANN Atresn'ng Officer (nmmissioner nfParems and Trademarks 

